The present invention relates to railway brake apparatus of the type employing a brake actuator in which dual pistons are tandem-connected, one being larger than the other and cooperating with the cylinder thereof to form an application chamber and a release chamber on the opposite sides in which compressed air is stored to develop the desired brake forces, without the need for separate, conventional storage reservoirs.
During brake release, compressed air is supplied to these storage chambers by a control valve device that is operative in response to variations in the train brake pipe pressure. When a brake application is initiated, the control valve device connects air from the release chamber of the larger power piston to the opposite side of the smaller positioning piston. A one-way check valve device is provided to effect pressure equalization between the opposite application and release chambers of the power piston to permit movement of the dual pistons in a brake application direction under the influence of the pressure acting on the positioning piston.
In application position of the tandem-connected dual pistons, the control valve device associated with the brake actuator exhausts the release chamber air on one side of the power piston to atmosphere to establish a pressure differential across the power piston and to accordingly produce the desired braking force.
Empty/load brake equipment is normally provided on railway trains to prevent sliding wheels and to more equally distribute car retardation forces throughout the train during braking, with respect to different car load conditions.
In the aforementioned referencing application, there is disclosed an empty/load arrangement, as shown in FIGS. 1 and 6 thereof, in which a two-position changeover valve is provided to sense the vehicle load condition according to the degree of deflection of the vehicle. In the "load" condition the release chamber air on the one side of the power piston is connected directly to atmosphere, while in the "empty" condition, this air is connected to atmosphere via a one-way check valve device. The value of a spring that normally biases the check valve closed determines the air pressure that is retained on the one side of the power piston to limit the pressure differential thereacross and accordingly establish the "empty" vehicle brake force. Since the spring characteristics are constant, the "empty" brake force reduction remains the same for any given reduction of brake pipe pressure, even though higher brake pipe charges may be carried where higher braking pressures are desired.